[3.15] gh-151238: Check for _get_resized_exprs failure in _PyPegen_{joined,template}_str (GH-151259) (#151344)

(cherry picked from commit 4b44b1e)

Co-authored-by: Stan Ulbrych <stan@python.org>

Author: miss-islington

Lib/test/test_fstring.py

@@ -593,6 +593,17 @@ def test_compile_time_concat_errors(self):
                              r"""b'' f''""",
                              ])
 
+    def test_concat_decode_failure_does_not_crash(self):
+        script = r'''
+import builtins
+builtins.__import__ = builtins  # Breaks warning machinery so _get_resized_exprs returns NULL
+try:
+    compile('"x"f"\]"b""', '<test>', 'exec')
+except Exception:
+    pass
+'''
+        assert_python_ok('-c', script)
+
     def test_literal(self):
         self.assertEqual(f'', '')
         self.assertEqual(f'a', 'a')

Misc/NEWS.d/next/Core_and_Builtins/2026-06-10-15-19-58.gh-issue-151238.C9Wu4x.rst

@@ -0,0 +1,2 @@
+Fix a crash when compiling a concatenated f-string or t-string if an error
+occurs when processing one of it's parts.

Parser/action_helpers.c

@@ -1416,6 +1416,9 @@ expr_ty
 _PyPegen_template_str(Parser *p, Token *a, asdl_expr_seq *raw_expressions, Token *b) {
 
     asdl_expr_seq *resized_exprs = _get_resized_exprs(p, a, raw_expressions, b, TSTRING);
+    if (resized_exprs == NULL) {
+        return NULL;
+    }
     return _PyAST_TemplateStr(resized_exprs, a->lineno, a->col_offset,
                               b->end_lineno, b->end_col_offset,
                               p->arena);
@@ -1425,6 +1428,9 @@ expr_ty
 _PyPegen_joined_str(Parser *p, Token* a, asdl_expr_seq* raw_expressions, Token*b) {
 
     asdl_expr_seq *resized_exprs = _get_resized_exprs(p, a, raw_expressions, b, FSTRING);
+    if (resized_exprs == NULL) {
+        return NULL;
+    }
     return _PyAST_JoinedStr(resized_exprs, a->lineno, a->col_offset,
                             b->end_lineno, b->end_col_offset,
                             p->arena);